Bearings are a vital part of innumerable types of equipment. Ball bearings and roller bearings can be found in nearly every type of machine and device with rotating parts. Roller bearings are frequently specified when shock and impact loads are present, or when a large bearing is needed. Both ball and roller bearings generally consist of at least four elements: inner and outer bearing rings (also known as races), the rollers (or balls) and a cage (or bearing separator). The "cone" of a bearing consists of three of these elements: the inner ring, rollers and separator. The construction and function of ball and roller bearing assemblies is familiar to those of ordinary skill.
Although bearings are precisely constructed, failure after a certain point is inevitable. Such failure may be caused by foreign objects or due to flaws in the bearing components themselves. Other failure modes are simply caused by wear. However, if the advent of failure is discovered, most bearings can be removed from service and refurbished or rebuilt prior to a catastrophic failure that would at the very least require replacement of the bearings. It has therefore become recognized that bearings can be visually inspected and the amount of wear can be determined both qualitatively and quantitatively to permit a decision to be made about the remaining useful life of a bearing.
A critically important application of bearings and bearing inspections is found in rail cars. The loads carried by the wheels and axles of rail cars are enormous and the efficiency of the rolling stock is directly affected by the condition of the bearings. For this reason, the Association of American Railroads (AAR) has set forth a detailed set of requirements and standards for the inspection of roller bearings. See Association of American Railroads, Mechanical Division, Roller Bearing Manual, Section 1, pp. H-II-1 through H-II-16 (Oct. 1, 1989), which is incorporated by reference as if fully set forth herein. The definitions and terms set forth in the above-referenced AAR Manual are hereby adopted for purposes of describing the present invention. However, the use of the present invention is not meant to be limited to the types of bearings described in the AAR Manual.
Presently, the standard method used for inspecting roller bearing cones is by visual inspection. To perform the inspection, a roller bearing cone is placed on a back lit inspection stand. The inspection stand holds the cone in a manner that permits it to be rotated, and illuminates the bearing from behind to permit an inspector to view portions of the bearing. The inner ring is then rotated and the rollers and inner raceway are visually inspected by observing the back lit areas. However, certain areas of the inner raceway are indented and cannot be seen using the back-lit method since they are located outside the line of sight of the inspector. In order to inspect those areas of the inner raceway that cannot be seen, a pointed feeler gage is held over the area while the cone is being rotated. A defect, e.g., a spall, will cause the feeler gage to transmit a slight mechanical vibration to the hand of the inspector. By virtue of experience, the inspector can determine whether the defect indicated is condemnable and constitutes a reason to repair the bearing, or scrap the cone if the defect cannot be repaired. There are two main disadvantages associated with the visual procedures currently used to inspect bearings. First, the back-lit viewing stands do not provide a clear view of every portion of the critical components of the bearing. Second, those portions of the inspection carried out using a feeler gage rely upon the sensitivity, experience and the subjective judgment of the inspector.
One attempt to provide improved rail car bearing inspections is known as the "Santa Fe" method, which involves a device analogous to a phonograph turntable that rotates a bearing while a stylus traces a path across the race surfaces. The deflections of the stylus provide an analog signal that can be displayed on an oscilloscope as a measure of the relative smoothness of the path traced by the stylus. Using this system, it is possible to detect certain types of flaws by quantifying the permissible level of deflection as measured on the oscilloscope scale. However, since this method cannot detect those types of flaws that do not exhibit surface deformations, it can only be used to reject bearings prior to undertaking the abovedescribed manual/feeler gage inspection.
Thus, there exists a need to provide improved methods and apparatus for inspecting bearings. It would be desirable to visually inspect the entire surfaces of critical bearing components. It would also be desirable to provide an inspection procedure that did not rely on the subjective judgment of the inspector to determine the degree to which a defect affects a bearing on the basis of "feel." Accordingly, it is an object of the present invention to provide an optical display system for inspecting bearings. It is a further object of the present invention to permit bearing inspections to be carried out more rapidly and with greater accuracy, thereby increasing the overall efficiency of the bearing inspection and rebuilding operation.